The present invention relates generally to optical analysis. More specifically, the invention provides a method and system for integrating optoelectronic systems and microfluidic systems. Merely by way of example, the invention has been applied to absorption spectroscopy and luminescence spectroscopy for microfluidic systems, but it would be recognized that the invention has a much broader range of applicability.
Microfluidic systems are usually analyzed with spectrometers. The effectiveness of spectrometers depends on structures of microfluidic systems. Microfluidic systems can be made of different materials, such as elastomer or semiconductor including silicon. These building materials affect the bandwidth available for spectroscopic analysis.
For example, microfluidic systems can be made of silicon. Silicon-based microfluidic structures usually suffer from the inability to perform optical analysis in the visible and near-ultraviolet spectral ranges. Due to the absorption edge of silicon, optical measurements in flow channels defined by silicon are usually limited to the infrared range and visible/ultraviolet spectroscopy is difficult to perform without using very elaborate geometries. For applications such as biochemistry, this difficulty poses a limitation since many absorption and fluorescence experiments are based on visible/UV fluorescent dyes.
In contrast, some elastomers are transparent in the visible and near ultraviolet spectral ranges. Hence elastomer-based microfluidic systems allow compact spectral analysis for chemical sensing and biological diagnostics. For example, fluorescently activated cell sorters based on pumps, valves and channels defined in RTV silicone elastomers have demonstrated excellent throughput and sorting accuracy. See A. Y. Fu, C. Spence, A. Scherer, F. H. Arnold, S. R. Quake, A microfabricated fluorescence-activated cell sorter, Nature Biotechnol. 17 (1999) 1109-1111. This article is hereby incorporated by reference for all purposes. These cell sorters have been fabricated inexpensively into very small and robust microfluidic devices. Chemical surface pretreatment of specific areas within a flow channel has led to the possibility of developing compact disease diagnostic chips, and even single molecule sizing systems can be built from elastomeric flow channels. In these applications, the overall size of the analysis system is typically limited by the dimensions of the optical excitation and detection components, and miniaturization of the readout optics is therefore desirable. However, miniaturization of grating-based spectrometer geometries is limited at least in part by a reduction of the spectral resolution, which can be predicted from the optical path lengths between the grating and the detection slit. For example, multi-wavelength 4 mm×12 mm spectrometers operating at 1500 nm typically yield a measured spectral resolution of approximately 1 nm. This compromise between resolution, insertion losses, and size usually limits the minimum size of such optical analysis systems.
Hence it is desirable to improve optical analysis techniques.